Borgmann Aquaponics Hydroponics
The Nitrogen Cycle in Aquaponics and Hydroponics
Understand the biochemical processes that provide nutrients to your plants
The Main Components of the Nitrogen Cycle
NH₄⁺ (Ammonium Ion)
The ammonium ion is the protonated form of nitrogen that dominates at low pH. It is produced by:
- Fish excretions (in aquaponics)
- Breakdown of organic matter
- Addition of fertilizers (in hydroponics)
Properties: Predominant at pH < 7, relatively non-toxic to fish, can be taken up directly by plants
NH₄-N (Ammonium Nitrogen)
This is a measurement unit that indicates only the nitrogen portion within the ammonium ion. Important for nutrient calculations:
Why important? Enables precise dosing and comparability of different nitrogen sources
Total Ammonium: NH₄⁺ + NH₃ (Henderson-Hasselbalch)
In water, a pH-dependent equilibrium exists between non-toxic ammonium (NH₄⁺) and highly toxic ammonia (NH₃). The Henderson-Hasselbalch equation describes this relationship:
| pH | NH₃ (%) |
|---|---|
| 7.0 | 0.5% |
| 8.0 | 4.5% |
| 9.0 | 25% |
Conclusion: pH control is crucial for the safety of your fish!
The Nitrification Process
The biological conversion of ammonium to nitrate occurs in two steps through specialized bacteria:
NH₄⁺
AmmoniumNO₂⁻
NitriteNO₃⁻
NitrateBacteria: Nitrosomonas, Nitrosospira
Reaction: 2 NH₄⁺ + 3 O₂ → 2 NO₂⁻ + 4 H⁺ + 2 H₂O
- Requires oxygen (aerobic)
- Produces acid (lowers pH)
- Nitrite is toxic to fish!
Bacteria: Nitrobacter, Nitrospira
Reaction: 2 NO₂⁻ + O₂ → 2 NO₃⁻
- Also aerobic (needs O₂)
- Nitrate is relatively non-toxic
- Main nutrient for plants
NO₃⁻ (Nitrate) - The Goal
Nitrate is the preferred nitrogen source for plants:
- Actively absorbed through roots
- Relatively non-toxic to fish (at moderate concentrations)
- Stable in water
- Indicator of a functioning biological system
Target Values:
- ? Aquaponics: 5-150 mg/L
- ? Hydroponics: 100-250 mg/L
Practical Tips for Your System
? Test Regularly
Measure NH₄⁺, NO₂⁻, and NO₃⁻ weekly to monitor nitrification.
⚖️ Control pH
Keep pH between 6.8-7.2 to maintain a safe NH₃/NH₄⁺ equilibrium.
? Ensure Aeration
Nitrification needs oxygen - ensure sufficient aeration in the biofilter.
Summary
The nitrogen cycle is a continuous biochemical process in which toxic ammonium (NH₄⁺) is converted by nitrifying bacteria via the also toxic nitrite (NO₂⁻) into plant-available nitrate (NO₃⁻). Understanding and controlling this process is crucial for the success of your aquaponics or hydroponics system.
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